Many newspapers covered the story that a new study has concluded there is limited evidence that mothers who occasionally binge drink damage their unborn babies. The Times reported the study as saying that “binge drinking during pregnancy has minimal effects on the unborn baby unless women make a habit of it.”

Most of the reports also advise that women use their common sense and do not use this finding as a licence to binge drink.

The news reports are based on research that combined the results of 14 studies that investigated the effects of drinking on the developing foetus and child. The studies included in the review varied considerably in their quality, methods, findings and whether or not they accounted for other factors that may have an affect upon birth outcome.

The research does not provide us with reliable evidence that it is safe to binge drink while pregnant. In the absence of reliable evidence women should continue to follow recommendations to drink minimal or no alcohol while they are pregnant.

Where did the story come from?

Jane Henderson and Ron Gray of National Perinatal Epidemiology Unit, University of Oxford, and Ulrik Kesmodel of University of Aarhus, Denmark, carried out this research. The study was supported by the Department of Health. The study was published in the peer-reviewedJournal of Epidemiology and Community Health.

What kind of scientific study was this?

The researchers looked through computer databases for all studies published between 1970 and 2005 that examined alcohol consumption by pregnant women and the outcome of their pregnancy, including birth weight, stillbirth, impaired foetal growth, or foetal alcohol syndrome.

The researchers only included studies where the amount of alcohol consumed was recorded in recognised terms of units or grams and there was some measure of “binge drinking”.

There were considerable differences between the methods used and so the researchers could not carry out a meta-analysis on the combined studies. They therefore gave a narrative discussion of their findings.

What were the results of the study?

Fourteen studies were considered relevant and suitable to be included in the analysis, and included research from the UK, USA, Australia, Denmark, and Canada.

The researchers found that the studies generally classified binge drinking as drinking five or more drinks on a single occasion, equivalent to 7.5 units or 60 grams of alcohol. However, some of the studies considered a binge to be less alcohol, others more, and one study included a time aspect in their definition (five or more drinks at least once a fortnight during pregnancy). Only some of the studies accounted for other factors (confounding factors) that may have affected the birth outcomes besides alcohol.

Seven of the studies examined foetal growth and weight and the researchers found no consistent links between binge drinking and reduced weight and growth. However, as the researchers acknowledge, they were unable to differentiate between binge drinking and heavy drinking within the studies. These studies were among those that had not considered confounding factors.

Three of the studies looked at foetal alcohol syndrome and found an increase in birth abnormalities associated with binging. However, one study had limited data and there were problems with the definition of binge drinking as this study considered it to be 10 units of alcohol. The studies had again not considered confounding factors.

Four of the studies looked at the intellectual and developmental outcomes of the children. These did find some difference in the outcomes of children of binge drinking mothers. However, the studies varied considerably in their length of follow up time and in the measures that they used to assess the children.

Two of the above studies found behavioural difficulties, and one study which followed the children of binge drinking mothers up to the age of 14 found that they had significantly more learning problems.

What interpretations did the researchers draw from these results?

The review authors conclude that they have found “no consistent evidence of adverse effect across different studies” on the foetus from binge drinking during pregnancy. However, there are possibly effects on a child’s intellectual ability, learning, and behaviour.

What does the NHS Knowledge Service make of this study?

Although this systematic review used reliable methods, the studies that were included within it varied considerably in their quality, methods and findings, and whether or not they accounted for factors that may have an effect on birth outcome other than binge drinking. The review’s conclusions are therefore subject to a number of problems.

The research does not provide us with reliable evidence that it is safe to binge drink whilst pregnant. One fundamental problem is that what was considered to be a “binge” was not the same in all of these studies. It is also unclear in many of the studies whether the effects of binge drinking were separated from other regular drinking or heavy drinking patterns, and other harmful exposures, such as smoking or other drugs.

Other factors that may have introduced error are the mother’s self-reporting of their drinking behaviour, differing times during the pregnancy that the drinking occurred, and the different measurement of the outcomes in the babies. Although findings on birth defects and growth restriction were inconclusive, the evidence did seem to point to a possible effect upon behaviour and intellectual development.

Based on this research, the statements in the newspapers that women should continue to follow recommendations to drink minimal amounts or no alcohol at all while pregnant are sensible. The review has clearly identified a deficit of knowledge specifically on the effects of binge drinking while pregnant, as opposed to regular drinking, and the researchers call for further research is justified.